1. Field of the Invention
The present invention relates to an image forming apparatus and a method of controlling heating of a fixing unit therein.
2. Description of the Related Art
Conventionally, in an image forming apparatus, a control unit and an engine control unit communicate signals regarding various information through a communication bus. When a power supply to the image forming apparatus is turned ON, or when the image forming apparatus returns to a normal mode from an energy saving mode, the communication bus is opened for communication such that heating of a fixing unit can be controlled based on the signals communicated through the communication bus. More particularly, the control unit determines whether it is necessary to heat the fixing unit and accordingly transmits an instruction to the engine control unit through the communication bus. Based on that instruction, the engine control unit controls heating of the fixing unit. Thus, to receive an instruction from the control unit, the engine control unit needs to wait for the communication bus to open. That results in slowing down the process of image forming.
To solve such a problem, Japanese Patent Application Laid-Open No. 2006-58824 discloses a technique in which an engine control unit independently controls heating of a fixing unit. That is, the engine control unit measures the temperature of the fixing unit and, when the temperature falls below a predetermined fixing temperature, controls heating of the fixing unit. Thus, it is possible to speedily activate the fixing unit.
However, if the temperature of the fixing unit is determined to be less than the predetermined fixing temperature when the power supply to the image forming apparatus is turned ON, or when the image forming apparatus returns to a normal mode from an energy saving mode, then the engine control unit controls heating of the fixing unit even if there is no instruction for image formation. That results in unnecessary power consumption.